Although cable television and communication systems have experienced extremely rapid growth, many areas, particularly urban, are still inaccessible because installations are inconvenient or impossible. Installation of cables in developed urban areas is difficult because of immovable construction and municipal regulations that require underground cables because external poles are no longer permitted. Cable operators are faced with either high costs of installation, or difficult installation in previously developed areas. Various municipal utilities, tunnels, underground ducts and other features of communities prevent the installation of cables.
A potential solution to these problems is over the air RF transmission for short distances, but restrictive regulations either prohibit such transmissions or make them costly and impractical. Licenses would be required, which are time consuming to obtain or unavailable.
To solve these problems various systems have been devised, some of which use light beams or laserlinks for line-of-sight transmissions. Previous systems, however, have been limited by narrow bandwidths and poor performance caused by mechanical stability limitations. Further, such transmissions have usually been limited to a few channels. Previously implemented systems are inadequate for the massive amounts of signal transmissions needed for a useful and efficient system.
Systems have been designed using laser beams for transmission of information, but to date they have achieved wide acceptance only over fiberoptic cables rather than through the atmosphere. Atmospheric systems suffered a variety of problems not the least of which were insufficient bandwidth, aiming problems, and poor mechanical stability. Added to these are the inherent safety hazards of laser beams to the eye which could make safe installation questionable. Federal regulatory agencies severly restrict the use of laser light beams at levels which might present a health hazard. It would be desirable if a system could be designed which took advantage of the wide bandwidths inherently available from laser beams, but which also could provide adequate safety at low cost.
It is, therefore, an object of the present invention to provide an electro-optical communications signal transmission system using a laser beam which is not a health hazard.
Yet another object of the present invention is to provide a communications signal transmission and distribution system that takes advantage of the extremely wide bandwidth of a laser beam.
Still a further object of the present invention is to provide a television and digital data transmission system which can be easily installed in urban areas where cables are inconvenient or impossible to use.
Still another object of the present invention is to provide a communications signal transmission system which uses a laser beam providing efficient signal transmission.
Still another object of the present invention is to provide a communications signal transmission system having a laser beam optic system which spreads beam energy to safe energy levels.
Still another object of the present invention is to provide a communication signal transmission system which uses a laser beam that provides an efficient signal to noise ratio at the receiver because the signal is not scattered.
Still a further object of the present invention is to provide a communications signal transmission system using a laser beam system which is effeciently modulated to provide a wide bandwidth.
A further object of the invention is to provide a laser beam transmission system having strong signal security as there are no stray signals.